Electronic Properties of Spin Controlled Semiconductor Nanostructures

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This group was formed to study and elucidate the electronic structure and the transport properties of spin-controlled semiconductoring materials and nanostructures. To this end, the growth and processing of ferromagnetic semiconductors and their related heterostructures, transport/magnetic/optical properties of these materials and structures, and the electronic structure calculation as well as the theory of transport properties were investigated. The summary of the research results is :1. Ferromagnetic/non-magnetic trilayer structures made of semiconductor showed spin-dependent scattering, interlayer coupling and tunneling magnetoresistance. Resonant tunneling diodes with (Ga, Mn) As emitter exhibited spontaneous current peak splitting below the ferromagnetic transition temperature. Also electrical spin-injection from ferromagnetic (Ga, Mn) As into a nonmagnetic GaAs structure was demonstrated. (H.Ohno et al.)2. Magnetism and transport in (In, Mn) As and (Ga, Mn) As at low temperature was studied. One of our important finding is that crystalline quality is much improved by heat treatment at comparatively low temperature. Soft X-ray absorption experiment is making it clear that the improvement is due to the evaporation of excess As atoms. (S.Katsumoto et al.)3. First-principle electronic band-structure calculations are carried on III-V based diluted magnetic semiconductors (Ga, Mn) As. The magnetic interactions between the nearest neighboring 3d transition-metal spins are ferromagnetic for V, Cr, Mn. (N.Suzuki et al.)We have prepared an artificial atom/molecular having a high-degree of rotational symmetry. For artificial atom, (i) atom-like properties such as shell filling and obeisance of Hund's rule and (ii) various transitions of spin states as a function of magnetic field have been observed. For artificial molecules we have investigated novel spin effects such as spin blockade, isospin blockade, spin-dependent tunneling, and so on. (Tarucha et al.)